Overview
First of all, you can find AH-D310 online for as little as $32, which makes them a very good deal. Possibly better than some $50-70 headphones, even. The "R" version has a microphone and IPod control, it's a bit more expensive, but worth it if you need that. So overall the headphones are a very good replacement for a mobile phone earset, for the money
AH-D310 are Denon's cheapest/lowest AH-D model, now that the AH-P372 have apparently been killed off. The OEM is, of course, Foster. The big difference with AH-P372 is, they don't fold into a ball, they fold flat (see attached photo). The other big difference is 42 mm. drivers instead of AH-P372 38 mm. drivers. In my view, 42 mm. drivers are a bit of a minus, as they don't have the balance between sweetness and power 38 mm. have. Just to give you an idea, AKG K-240 Sextett and first-edition K-141 headphones had 38 mm. drivers, and they're one of the "golden standards" on Head-Fi.
AH-D310 are obviously designed for weak players/mobile phones. Out of a Roland UA-1G USB interface, they tend to get overly bassy/boomy, but with a measly Nokia C3 phone they play great. So if you were looking for a headset, AH-D310R or AH-D510R might be just the thing.
Sound
The best way to describe AH-D310 is "supra-aural cheap sibling to AH-D1001". And Creative Aurvana Live, Denon AH-D1000, AH-D1100, etc. Fast trademark dynamics, great sensitivity (you can use them to check for hiss/background noises), nice detail. But less air/ambience than AH-D1001. Sounds like AH-D1001, but more congested, with a smaller soundstage, and with less sparkle. Soundstage is smaller than AH-D1001, obviously. Instrument separation is a tad worse. The problem here is, cups are too small, so there's not enough space for ears to produce enough "air" to the sound. They're also bassier. The curious bit is that apparently the headphones were designed for weak players, as they don't get to be that bassy with a weak headphone out, like that of a Nokia C3 phone.
As with almost all Asian headphones, AH-D310 aren't very fond of the third octave (~220 Hz), which is an issue for electric guitar music. The low midrange drop sucks out some detail and makes guitars sound emptyish. So you have to boost the 220 or 250 Hz slider on your player's EQ. Funnily, they work just fine with the phone (though this is after modding with Senn HD414 foam and a new cable).
So yes, midrange could use a bit more detail, but overall sound quality is pretty good, and the speed of Foster diaphragms makes AH-D310 play very lively. Bear in mind that this is talking more about the modded AH-D310; stock cable, as with all Denon headphones, doesn't do them justice.
They're not that great for playing music (as in, actually playing a synthesiser) as there's some midrange honkiness when midrange is overloaded with, say, virtual analogue (or real analogue) pads. Again, for weaker players and phones this isn't an issue as they simply don't have the power to overload AH-D310 to honk, but the sneaky suspicion is, that's refraction from the plastic driver grilles.
Recommended EQ for a more powerful player is: drop bass by one slider, boost low midrange (~250 Hz) by one slider.
Build & Comfort
AH-D310 are halfway between supra-aural and circumaural. They could be called "smallish circumaural", but they do not leave much air between the rear parts of ears and the drivers, which is responsible for the somewhat congested sound and lack of air in sound. AH-D1001, -2000, etc. all have larger cups with more space for ears, so ears get the full sound picture. Ears have to be fully exposed to the sound source for a realistic soundscape; cramming them into smallish cups denies some of the exposure.
Cups rotate on hinges and make the headphones fold flat (see photo). They look more fragile than they really are. Headband is metal with pleather/foam padding, and the whole setup is plastic.
Earpads are memory foam, and for the first couple weeks they might even hurt slightly on the ear rears, Later on they adjust and don't bother, but comfort-wise they're somewhere in-between supra- and circumaural too. AH-D310 might be large enough for a fragile Asian girl to call them "circumaural", but for a European male they're a tad too small.
Isolation
Not that much, actually. The cups are empty inside. No isolation materials or anything. They do attenuate external sounds, but with a weakish phone they'll freely pass traffic/people noise. With a more powerful player (or a sound interface like Roland UA-1G) they isolate by sheer loudness.
Modding
Mine have the full Mark L-style modding: silver-plated copper twisted pair (AWG 30) recable, Sennheiser HD414 foam to "sweeten out" the sound a bit (and boost midrange), Dynamat stabilisation, and cup filling. Which makes them pretty nice headphones actually, for not that much money. A lot warmer and livelier than any stock headphones, even those costing three times as much. They're the regular version, not "R", so no microphone or player control, but then it's not that needed.
One thing though: they can be hell to work with as the cup screws were driven in hard and deep at the factory. So the only way they could be extracted was with a screwdriver held with pliers. And that took hours.
Summary
Nice headphones for modding, in spite of dead-incrusted screws
Also a good headset, though as it's wired for IPhones, it may not work with all mobile phones. The modded version is quite impressive, but then that's silver-plated wiring+Foster diaphragms. However, if you're interested in modded Foster headphones, then AH-D1000, AH-D1001, AH-D1100, and Creative Aurvana Live are a better value, as they're true circumaural and have more ambience/sparkle. Also more comfortable.
Long story short, this is a good buy. Recommended.
